Geochronology and Geochemistry of the Lingtse Gneiss, Darjeeling - Sikkim Himalaya: Revisited

Foliated augen gneisses with streaky character, such as the Lingtse Gneiss of Sikkim-Darjeeling area, occur throughout the Himalaya. The Lingtse Gneiss is highly deformed and Occurs as thin tabular bodies. Considerable textural variation is noticed depending on the intensity of deformation and grain growth. The rocks are peraluminous and show fractionated REE pattern (La_n/Lu_n = 1.2-6.8). These gneisses were previously dated at 1075 and 2034 Ma by Rb-Sr method. The results of the present isotopic age determination by Rb-Sr and Pb/Pb methods indicate ages of 1678 ± 44 Ma and 1792 ± 45 Ma respectively. The variability and scatter of isotopic composition are believed to reflect imprints of tectono-thermal events.